This invention relates to fire suppression mechanisms using vaporizable liquid fire suppressant, for example monobromotrifluoromethane, referenced in the literature as Halon 1301. This liquid material has very desirable fire-suppressant properties, e.g., low toxicity and physicochemical inhibition of the combustion reaction; or as a "chain breaking" agent, meaning that it acts to break the chain reaction of the combustion process. (National Fire Prevention Association, NFPA-12A National Standards Halon-1301 Fire Extinguishing Systems). However, the material has a relatively low boiling point of about minus 72.degree. F., and a vapor pressure of about 215 p.s.i. at 70.degree. F. These characteristics present the problem of excessive vaporization and flashing when the material is discharged as a thin jet stream from a nozzle toward the flame to be suppressed. As the thin liquid stream moves from the nozzle the stagnant ambient air tends to mix with the concentrated stream to diffuse or dissipate the stream. Additionally the mixed-in air heats the liquid stream to vaporize some of the suppressant liquid before it reaches the flame to be suppressed. Finally, the heat generated by the flame tends to further vaporize and dissipate the suppressant material before it can reach the flame zone. Intense heating of an air mass can create a strong thermal draft or wind, which can mechanically deflect the suppressant stream before it becomes effective on the flames. In some cases for example with portable extinguishers using Halon 1301, the liquid stream begins to dissipate at only about four feet from the nozzle. With other halogenated hydrocarbon fire suppressant material such as Halon 1211, the penetration range is somewhat greater, but at the expense of a more lethal toxicity factor. In any case, the penetration distance is somewhat affected by the intensity of heat generated by the flame; high temperatures outward from the flame area can vaporize or dissipate the suppressant before it is effective on the flame.
The principal object of the present invention is to increase the effective penetration range of a thin vaporizable liquid fire suppressant stream discharged from a nozzle. Preferred suppressant is monobromotrifluoromethane. The nozzle is constructed to form a coolant shroud (air or vaporizable liquid) around the fire suppressant jet stream. An important feature of the invention is that the coolant shroud is formed before the fire suppressant emerges from the nozzle; the nozzle includes an internal liquid-attachment wall structure that orients the liquid into a thin jet before the liquid reaches the nozzle exit opening. An internal free space exists within the nozzle for accommodating the shroud-forming material. Suppressant comes out of the nozzle at least partly surrounded by an insulating coolant shroud.
The coolant shroud travels with the jet stream for at least part of its travel to the fireball, thus shielding the jet stream from thermal contact with the stagnant ambient atmosphere. Thermal vaporization and flashing of the liquid in the jet stream is minimized, thereby enabling the jet to travel a relatively long distance before dissipating to a spent condition.
Hopefully the invention will make it possible for a human to operate a portable fire extinguisher while standing a relatively long distance from the flame; this is advantageous in that there is less likelihood that the intense heat will drive the human back from the flames to a point where he cannot deliver the suppressant to the most intense part of the flame where combustion inhibition is most necessary.
It is contemplated that the nozzle orifices will be relatively small to produce a relatively concentrated jet stream of liquid fire suppressant. Such a stream can be thermally shielded from the atmosphere by a sacrificial shroud, thereby enabling a high percentage of the suppressant liquid to impinge on and into the flame, rather than being spent before reaching the flame area. The desired concentrated stream can be aimed at the precise point where the flame is most intense.